Sandea, Valor, and Outlook offered promising results in different combinations applied preemergence (PREE). The combination of Prefar plus Sandea gave 95% control of pigweed and continued to control lambsquarters at 90% late in the season. Prefar combined with Valor gave acceptable pigweed control and lambsquarters were controlled at acceptable levels at 88 and 86%, respectively. Outlook combined with Valor was safe and gave good early pigweed control and later control of lambsquarters. Strategy alone at either 1.0 or 2.0 pt/A did not provide acceptable levels of weed control and no significant crop injury was observed.

Nicosulfuron, quinclorac, triflusulfuron, MKH-3586, pyraflufen, and tribenuron applied PREE appeared to be safe on the lettuce crops while demonstrating variable activity against weeds. Head lettuce and romaine were not as tolerant to POST herbicides compared to PREE herbicides. Sulfosulfuron, MKH-3586, rimsulfuron, ethametsulfuron and pyraflufen applied POST caused various degrees of injury on the lettuces that were less injurious than other treatments. Thifensulfuron, nicosulfuron, and quinclorac applied PREE or POST showed acceptable broccoli tolerance. Ethametsulfuron exhibited adequate safety when applied POST on broccoli. Thifensulfuron, nicosulfuron, and quinclorac applied PREE also showed spinach tolerance. Similar to head lettuce and romaine spinach was not as tolerant to POST herbicides compared to PREE herbicides.

Seventeen herbicides recently gaining registrations in corn, soybeans, or other major crops were evaluated in screening tests for potential use in melons. In a preemergence herbicide screening test, flumioxazin, dimethenamid, halosulfuron, and s-metolachlor demonstrated melon crop safety at rates higher than rates for effective weed control. In a postemergence screening test, halosulfuron and rimsulfuron gave acceptable weed control with adequate crop safety. Flumetsulam and thifensulfuron appeared to offer some acceptable weed control with a very narrow margin of crop safety. Herbicides that did not offer adequate melon crop safety or acceptable weed control in the screening tests were carfentrazone, sulfentrazone, cloransulam, flumiclorac, fluthiamide/metribuzin, imazamox, isoxaflutole, triflusulfuron, primisulfuron/prosulfuron, and clomazone.

Halosulfuron and sulfentrazone were not safe to carrots at the lowest rates tested at 0.025 and 0.188 lb AI/A, respectively. At 20 DAT, halosulfuron at 0.038 to 0.075 lb AI/A gave better than 92% control of nutsedge in carrots. Nutsedge control was 77 to 80% at 20 DAT sulfentrazone applied at 0.188 to 0.375 lb AI/A. Both herbicides demonstrated slow activity against nutsedge during the first 7 DAT and then progressed to reduce weed growth at 13 to 20 DAT. Sulfentrazone appeared to act slightly faster than halosulfuron but showed maximum activity at 13 to 20 DAT.

Halosulfuron at rates ranging from 0.05 to 0.10 lb AI/A with no adjuvant added to the POST application spray did not cause any injury to watermelons. Halosulfuron did not appear to cause significant crop injury earlier in the season to reduce marketable fruit yield at harvest. Halosulfuron was highly effective against London rocket but did not control purslane or groundcherry. Weed control efficacy was improved significantly when Latron CS-7 or Activator-90 was added to halosulfuron at either 0.05 or 0.075 lb AI/A. LI-700 did not improve the activity of halosulfuron over the treatments without an adjuvant.

In preemergence (PREE) herbicide testing, all three lettuces, head, romaine, and red leaf, exhibited some tolerance to carfentrazone, sulfentrazone, flumetsulam, rimsulfuron, and thifensulfuron while giving effective weed control. In postemergence (POST) testing, cloransulam and flumetsulam controlled weeds at the lowest applied rates while lettuces were safe to cloransulam at 0.01 lb AI/A and flumetsulam at 0.03 lb AI/A. Imazamox was safe on lettuces at 0.01 lb AI/A and controlled weeds at 0.007 lb AI/A. For broccoli, sulfentrazone, fluroxypyr, and thifensulfuron applied PREE demonstrated reasonable safety and weed control. Cloransulam, flumetsulam, and fluroxypyr applied POST on broccoli exhibited adequate crop safety and good weed control.

No description available.

No description available.

Ragwort (Jacobaea vulgaris syn. Senecio jacobaea), a common weed of pasture and poorly managed land worldwide, is toxic to livestock and horses. There is no fully satisfactory control option available. The aim of the work described in this thesis was to assess the potential of root infecting pathogens to cause disease in ragwort, and to examine the possibility of using them as biological control agents against this weed. Thirty-six root infecting isolates were obtained from ragwort roots, collected from a nationwide postal survey where Pony Club adult leaders were asked to provide samples. Twenty-one of these were identified as Fusarium spp. by morphological identification and tested for the ability to cause disease on aseptically raised ragwort seedlings. Twelve isolates demonstrated virulence towards ragwort when measured by disease score over a 14 day period. These isolates were identified by molecular means using the internal transcribed spacer and translation elongation factor genes, as either Fusarium avenaceum or F. acuminatum while isolates of F. solani, F. redolens, F. cerealis or F. culmorum did not exhibit virulence except one isolate of F. culmorum which was weakly virulent. To investigate the biological control potential of virulent isolates, a representative of F. avenaceum and F. acuminatum plus the one weakly virulent F. culmorum isolate, were tested against plants of agricultural importance in grasslands. Six grasses (crested dogs tail, Cynosurus cristatus; Timothy, Phleum pratense; red fescue Festuca rubra; Italian ryegrass, Lolium multiflorum; and two varieties of perennial ryegrass, L. perenne) were unaffected by inoculation with any of the isolates. There was no significant difference between the symptoms caused by F. avenaceum and F. acuminatum on ragwort, red clover (Trifolium pratense) and white clover (T. repens). F. culmorum was more virulent towards white clover than either red clover or ragwort. This suggests that although high concentrations of pure PA may inhibit fungal growth, the range of other nutrients in the plants can counteract this negative effect.

Master of Science / Department of Agronomy / Mithila Jugulam / Extensive, often exclusive, use of glyphosate in crop production has resulted in evolved glyphosate resistance in several weed species globally. Kochia is a competitive summer annual weed, well adapted to the North American Great Plains and has recently evolved resistance to glyphosate by gene amplification of 5-enolpyruvyl shikimate 3-phosphate synthase (EPSPS), the target-site of glyphosate. The overall objective of this research was to investigate the genetic basis of glyphosate resistance in kochia, specifically to study 1) the inheritance of glyphosate resistance and 2) determine the chromosomal distribution of EPSPS gene copies. Homozygous resistant (R) and susceptible (S) parental lines of kochia were identified. Using these parents, reciprocal crosses were performed to produce F₁ progeny. As expected for a nuclear encoded EPSPS gene, F₁ plants from both crosses survived various doses of glyphosate application. However, F1 plants showed intermediate shikimate accumulation and EPSPS gene copies (relative to ALS reference gene) compared to parents. F₂ progeny were produced by selfing F₁ plants. In response to 870 g ae ha⁻¹ glyphosate, F₂ plants (n=115) segregated into 3:1 (R:S) implying a Mendelian monogenic segregation of glyphosate resistance in kochia. Additionally, relative EPSPS gene copies ranged from 1-10 in the F₂ progeny (n=51) with a genotypic segregation of 40:11 (plants with 3 or more EPSPS gene copies: plants with 1 EPSPS gene copy). In F₂ dose-response, a correlation between the level of resistance and relative EPSPS gene copies was observed. Genomic organization of the amplified copies using fluorescent in situ hybridization (FISH) displayed a single and larger hybridization site of the EPSPS gene on one pair of homologous chromosomes in R compared to a faint hybridization site in S samples of kochia. These results suggest possibility of amplification of EPSPS gene mediated via unequal recombination leading to the evolution of the glyphosate resistance in kochia.